Soft x-ray spectroscopy experiments on the near K-edge of B in MB2 (M = Mg, Al, Ta, and Nb) - art. no. 174504

Soft x-ray-absorption and emission measurements are performed for the K-edg e of B in MB2 (M = Mg, Al, Ta, and Nb). Unique feature of MgB2 with a high density of the B 2p(xy)(sigma) state below and above the Fermi edge, which extends to 1 eV above the edge, is confirmed. In contrast, the B 2p density of states in AlB2 and TaB2, both of occupied and unoccupied states, decrea sed linearly towards the Fermi energy and showed a dip at the Fermi energy. Furthermore, there is a broadening of the peaks with p sigma character in x-ray emission spectra and x-ray-absorption sepctra of AlB2, which is due t o the increase of three dimensionality in the p sigma band in AlB2. The den sity of states (DOS) of NbB2 has a dip just below the Fermi energy. The pre sent results indicate that the large DOS of B-2p sigma states near the Ferm i energy are crucial for the superconductivity of MgB2.